Seminar

Time is a fundamental quantity determining transport and reaction progresses in hydrologic and hydrogeological systems. Travel time distribution (TTD) is a lumped representation of discharge and solute export responding to input events in a system. It encapsulates storage dynamics and transport process into a single mathematic function, and resolves mixing process by differentiating water in discharge into a series of water parcels with different ages or from different historical input events. The TTD theory provides a powerful tool to study transport and reaction processes in a time-integrated Lagrangian perspective. The properties of TTD and the theoretic relation between TTD and transport are investigated in this study. To link TTD with both conservative and reactive transport in aquifers, a general framework based on Green’s function is proposed. This framework unifies the theories of travel time distribution and reactive transport and gives a guide on field studies of time-controlled transport problems. A multi-fidelity model is developed to explore the influence the internal variability of groundwater flow system on time-variant TTD. In Lake Taihu, travel time is of importance determining biogeochemical and ecological processes in the lake. Long-term deuterium isotope data in the lake and rivers connected to the lake are used to evaluate the time-variant TTD of lake water. The travel time ranges from 4-8 months in dry season and 2-5 months in wet season. Lake Taihu shows an inverse storage effect, i.e., more young water is released when lake volume is large, and vice versa. The long-term monitored flow rate data and water chemistry data in Po Shan hillslope indicate that the temporal variation of TTD and storage selection preference are different from those in natural hillslopes. In wet season, some sub-vertical drains may drain additional old water to the tunnels, which may accelerate the chemical weathering process in hillslope.